1. Field of the Invention
This invention relates to a vibrating gyroscope, and more particularly to a vibrating gyroscope which can be applied in, for example, a navigation system for detecting the position of a mobile body by detecting its rotational angular velocity and carrying out appropriate course corrections, or in a vibration eliminating system, such as a shake-prevention device, for detecting a rotational angular velocity caused by external vibration such as shaking.
2. Description of the Related Art
FIG. 8 is a diagrammatic view of an example of conventional vibrating gyroscope. The vibrating gyroscope 1 shown in FIG. 8 comprises a vibrator 2. The vibrator 2 comprises a vibrating body 3 having a square rod-shape. The vibrating body 3 comprises a thin-strip-shaped first piezoelectric substrate 3a and a second piezoelectric substrate 3b which are laminated and affixed together. As shown by the arrows P in FIG. 8, the first piezoelectric substrate 3a and the second piezoelectric substrate 3b are polarized in opposite directions parallel to their thickness. A common electrode 4 is provided as an driving electrode on a main face of the first piezoelectric substrate 3a. Furthermore, two divided electrodes 5a and 5b, as two detecting electrodes are provided on a main surface of the second piezoelectric substrate 3b so as to be spaced apart along a longitudinal direction of the main surface of the second piezoelectric substrate 3b. Moreover, an intermediate electrode 6 is provided between the first piezoelectric substrate 3a and the second piezoelectric substrate 3b. 
The two divided electrodes 5a and 5b of the vibrator 2 are connected with two input terminals of an adder circuit 7. The output terminal of the adder circuit 7 is connected to the input terminal of an oscillator circuit 8. The output terminal of the oscillator circuit 8 is connected to the common electrode 4 of the vibrator 2. Furthermore, the two divided electrodes 5a and 5b of the vibrator 2 are connected via resistors 9a and 9b to a middle point forming a reference voltage, such as a middle voltage which is a half voltage of the power voltage. Moreover, the two divided electrodes 5a and 5b of the vibrator 2 are connected to two input terminals of a detection circuit 10 comprising a differential amplifier.
In the vibrating gyroscope 1 shown in FIG. 8, a drive signal is output from the oscillator circuit 8 via the adder circuit 7, and is applied to the common electrode 4 of the vibrator 2. This drive signal causes the first piezoelectric substrate 3a and the second piezoelectric substrate 3b to vibrate reversely together, and as a result, the vibrator 2 vibrates at a right angle to the main faces of the first piezoelectric substrate 3a and the second piezoelectric substrate 3b. When the vibrator 2 is not rotating, similar detection signals are obtained from the divided electrodes 5a and 5b. Then, when a rotational angular velocity other than zero around the center axis of the vibrating body 3 is added to the vibrator 2, the Coriolis force changes the direction of the vibration of the vibrator 2, whereby detection signals corresponding to that rotational angular velocity are obtained from each of the two divided electrodes 5a and 5b. In this case, in correspondence with the rotational angular velocity, for instance, the voltage of the detection signal from one divided electrode 5a increases, and the voltage of the detection signal from the other divided electrode 5b decreases. Therefore, in this vibrating gyroscope 1, it is possible to detect the rotational angular velocity using the signal between the divided electrodes 5a and 5b, that is, the output signal of the detection circuit 10.
However, when a vibrating gyroscope such as the vibrating gyroscope 1 shown in FIG. 8 is miniaturized and its power voltage is reduced, the amplitude of the vibrations of the vibrator decreases, lowering the sensitivity of the vibrator. When the sensitivity of the vibrator of the vibrating gyroscope is lowered in this way, the S/N (signal to noise ratio) of the output signal of the vibrating gyroscope deteriorates, and the resolution also worsens. In particular, noise in the S/N in this case is mainly circuit noise and the like.
Furthermore, in a vibrating gyroscope, it is desirable that the temperature characteristics of the sensitivity can be easily altered.
The present invention can solve the aforementioned problem associated with the conventional art and provides a vibrating gyroscope which has a sensitivity and/or an adjustable temperature characteristics of the sensitivity.
The vibrating gyroscope comprises a vibrator having an driving electrode and two detecting electrodes; first drive means for applying a first drive signal to the driving electrode; second drive means for applying a second drive signal having the phase of the drive signal, or a phase obtained by inverting the phase of a detected signal detected from the two detecting electrodes, to the detecting electrodes; and detection means for detecting a detected signal in correspondence with the rotational angular velocity from the two detecting electrodes.
In the vibrating gyroscope according to the present invention, the first drive means for instance comprises an adder circuit, two input terminals thereof being connected to the two detecting electrodes, and an oscillator circuit, an input terminal thereof being connected to the output terminal of the adder circuit, and the output terminal thereof being connected to the driving electrode.
In the vibrating gyroscope according to the present invention, the second drive means for instance comprises a phase inversion circuit, an input terminal of the phase inversion circuit being connected to the output terminal of the adder circuit, and the output terminal being connected via two resistors to the two detecting electrodes.
In the vibrating gyroscope according to the present invention, the second drive means comprises for instance a phase inversion circuit, an input terminal of the phase inversion circuit being connected to the output terminal of the oscillator circuit, and the output terminal being connected via two resistors to the two detecting electrodes.
In the vibrating gyroscope according to the present invention, the second drive means comprises for instance an impedance conversion circuit, the input terminal thereof being connected to one of the two detecting electrodes; and a phase inversion circuit, an input terminal of the phase inversion circuit being connected to the output terminal of the impedance conversion circuit, and the output terminal being connected via two resistors to the two detecting electrodes.
In the vibrating gyroscope according to the present invention, the second drive means such as a phase inversion circuit may be given predetermined temperature characteristics, in order to give desired temperature characteristics to the applied voltage of the other drive signal.
In the vibrating gyroscope according to the present invention, the first drive means applies a first drive signal to the driving electrode of the vibrator, and second drive means applies second drive signal to the two detecting electrodes of the vibrator, these drive signals having reverse phases, thereby increasing the amplitude of the drive signal applied between the driving electrode and the two detecting electrodes of the vibrator. Since the amplitude of the drive signal applied to the vibrator increases in this way, the sensitivity of the vibrating gyroscope is higher, its S/N improves, and its resolution is better thereby realizing a vibrating gyroscope having a small body or a vibrating gyroscope which can be operated with a low supply voltage.
Furthermore, in the vibrating gyroscope according to the present invention, when for instance the phase inversion circuit or the like is given predetermined temperature characteristics in order to give desired temperature characteristics to the applied voltage of the other drive signal, sensitivity having the desired temperature characteristics is obtained. Therefore, in the vibrating gyroscope according to the present invention, it is possible to easily change the temperature characteristics of sensitivity.
For the purpose of illustrating the invention, there is shown in the drawings several forms which are presently preferred, it being understood, however, that the invention is not limited to the precise arrangements and instrumentalities shown.